Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from wind using known foil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
Wind turbine rotor blades generally include a body shell formed by two shell halves of a composite laminate material. The shell halves are generally manufactured using molding processes and then coupled together along the corresponding ends of the rotor blade. In general, the body shell is relatively lightweight and has structural properties (e.g., stiffness, buckling resistance and strength) which are not configured to withstand the bending moments and other loads exerted on the rotor bade during operation. To increase the stiffness, buckling resistance and strength of the rotor blade, the body shell is typically reinforced using one or more structural components (e.g. opposing spar caps with a shear web configured therebetween) that engage the inner surfaces of the shell halves.
The spar caps may be constructed of various materials, including glass fiber laminate composites and carbon fiber laminate composites. More specifically, modern spar caps are often constructed of pultruded composites that are less expensive than traditional composites, as the pultruded composites can be produced in thicker sections. The terms “pultruded composites,” “pultrusions,” or similar terms are generally used to define reinforced materials (e.g. fibers or woven or braided strands) that are impregnated with a resin and pulled through a heated stationary die such that the resin cures or undergoes polymerization. As such, the pultrusion process is typically characterized by a continuous process that produces composite parts having a constant cross-section. Thus, a plurality of pultrusions can be vacuum infused together in a mold to form the spar caps.
The industry is seeking ways to incorporate pultrusions into the spar caps of wind turbine blades for the material and economic benefits of such materials. For example, U.S. Patent Application Publication 2014/0271198 is directed to segmented wind turbine blades, wherein each blade segment includes a respective spar. The spars are connected together at spar joints, such as finger-type joints. The spar elements include planks manufactured as pultrusions, wherein first planks and second planks have different material compositions.
Accordingly, there is an ongoing need for an improved pultruded spar cap and method for incorporating such spar cap in a wind turbine blade, wherein such need may include optimizing the amount of more expensive and less expensive materials used in the spar cap to achieve a more cost efficient structure.